The present invention relates to an internal combustion engine controller designed to raise the temperature of a catalyst device by retarding ignition timing.
A catalyst device used in an exhaust system of an internal combustion engine for purifying exhaust gas demonstrates its purification function when the temperature is raised to a predetermined activation temperature. Therefore, when the temperature of the catalyst device is low such as when the engine is started, temperature rise control is performed on the catalyst device by retarding the ignition timing to raise the exhaust gas temperature so that the catalyst device is activated rapidly.
To diagnose whether or not a command value that is set by an ignition timing controller is set to an appropriate value for warming up the catalyst device, that is, to determine whether or not the temperature rise control of the catalyst device is actually being carried out, Japanese Laid-Open Patent Publication 2001-132519 describes an example of an apparatus that monitors whether or not an ignition timing set to a predetermined timing when warming up a catalyst device is within a predetermined range.
In the apparatus described in the above patent publication, the temperature rise control is performed using a crankshaft angle value, which indicates the ignition timing. This may lead to the problems described below.
The ignition timing is set basically in correspondence with engine operating conditions. Thus, the crankshaft angle, which indicates the ignition timing, may temporarily assume a value outside the predetermined range even if the temperature rise control is being executed. If a sufficient period is ensured for retarding the ignition timing during the temperature rise control, the temperature of the catalyst device is sufficiently raised even if the amount of retardation of the ignition timing temporarily falls below the required level. However, the apparatus described in the above patent publication may erroneously diagnose that there is an anomaly in the temperature rise control due to temporary fluctuation of ignition timing even though the temperature of the catalyst device is being raised sufficiently by the temperature rise control.